[TagsFileItemAction] Hide tags action if XAttrs are not supported
Summary:
Showing the tagging menu when no tags can be added to the file is
pointless, and adding a tag would silently fail.
Test Plan:
create a file on e.g a FAT filesystem
try to add a tag
Reviewers: Baloo, Dolphin, nicolasfella, ngraham, elvisangelaccio
Reviewed By: nicolasfella
Tags: Baloo
Differential Revision: https://phabricator.kde.org/D20858